if you see light and fire in me (I'll be your enemy)
by Hraap
Summary: It hadn't been a surprise when Katsuki had presented as an Alpha, or when Izuku had followed as an Omega. What had been surprising was Katsuki's solid refusal to allow Izuku's Quirklessness to stop him from dragging the younger boy up to his level, and making him into something more than just a worthless Deku.


_If you see light and fire in me (I'll be your enemy)_

 **Summary:** It hadn't been a surprise when Katsuki had presented as an Alpha, or when Izuku had followed as an Omega. What had been surprising was Katsuki's solid refusal to allow Izuku's Quirklessness to stop him from dragging the younger boy up to his level, and making him into something more than just a worthless Deku.

It's a change that follows Izuku through his whole life, one that marks him every step of the way. And it all starts with a dusty old book in the back of the public library.

0-0-0-0-0-0

From the time he was born, Katsuki Bakugou was practically assured to present as an Alpha.

"Just like his mother," his father would joke at parent-teacher conferences, when Katsuki's _difficult_ nature would often come up, along with all the wonderful little side-stories, like how easily he took up the role of leader in group projects, how all the kids clustered around him and wanted to play. All encouraging signs of a budding Alpha, and a strong one at that.

So when he _did_ present as an Alpha shortly before his doctor visit to check for the sign that would tell whether he would gain a Quirk or not, nobody was terribly surprised.

Likewise, when Izuku Midoriya of the _same_ class had presented as Omega not three days later, nobody had been surprised. The boy was softhearted and kind and had no issue with following Katsuki's whims, no matter how strange they might get on the day-to-day basis. He also had a natural inclination to care for those around him, all signs of a good, strong Omega.

That being said, the teachers were still quick to separate the two and keep a sharp eye on Katsuki after that. Young Alphas had a tend to revel in that first burst of power, and were at the mercy of their instincts, which were usually to scent-mark any Omega in the area and keep them away from any potential challengers. They also tended to want to dominate any "lesser" ranked males in a show of strength.

Little by little, the rest of the students presented after that. There were brief spats of arguments between the children as they tried to fight each other for rank in the growing baby hierarchy of the classroom. Two more boys and a girl presented as Alpha, and all three of them wrestled briefly with Katsuki for the role of dominant Alpha, only to be soundly beaten. But mostly the classroom was a balance of Betas and Omegas, and the trouble was kept to a minimum.

The next year was different. And not just because the children came back more sure of themselves, more entrenched in their roles as Alpha, Beta or Omega. It was because Bakugou's Quirk manifested and Midoriya's didn't, and it took all of a week before the whole school knew that Midoriya Izuku was Quirkless. That should have been the moment Bakugou turned up his nose and walked away from the boy, because no Alpha would tolerate weakness around them, and Quirklessness was known to break friendships as easily as a bull in a china shop.

Except… Katsuki didn't _care._

Well, no, he cared. Just not the way most Alphas would. Instead of pushing Izuku away, he started pushing the boy to be _better._

" _Stupid Deku, hurry up and score a goal already!"_

" _Deku, don't you dare fall behind!"_

" _Deku, if you don't hurry up and eat the rest of us are gonna go on without you!"_

" _Move, Deku, or be moved."_

And when Miyo-chan and the other two Alpha girls in the class decided to shove Izuku down and push him around and attempt to dominate him, rather than rushing in and baring his teeth in a show of possession towards his Omega, Katsuki watched Izuku with narrowed red eyes.

" _What the hell are you waiting for, Deku? Get up and punch them in the mouth already. I'm not gonna be late because you feel like being lazy."_

And… Izuku _had._ He'd gotten up, and when Miyo had swaggered towards him and attempted to dominate him again, he'd shoved her - _hard_ \- and bared his own teeth at them in a challenge. And then he'd _won_ that challenge, and gone back to Katsuki, who'd looked satisfied, and gotten to class before the bell could ring.

After that, the class left Izuku alone. It didn't stop the teachers wondering just what the hell they were witnessing - because Katsuki was prickly at his best and downright hellish at his worst, and realizing the boy he spent so much time around was _Quirkless_ on top of being an Omega should have sent him looking for better prospects. All the books written on the subject of Quirklessness ran in line with that thought process, at least.

And yet here Katsuki was, forcibly dragging Izuku around, demanding he follow and keep up with the rest. Pushing and demanding results, and Izuku following like he always did, shoving himself up and striving to be _whatever_ it was Katsuki wanted out to him. It was almost frightening.

It only got worse the year after that. Whatever plans Bakugou made for Midoriya were in full swing, and like a train running wild on the track, refused to be stopped. Even speaking to the parents yielded no results - Inko Midoriya was of the mind that so long as her son was happy and neither of the children were getting hurt, it was fine.

Mitsuki Bakugou on the other hand took one look at the way her son bossed Izuku around and snorted. "Should have seen that coming. Katsuki's never been a _quitter,_ especially not when his own are concerned. You lot can relax - he's fine, they're fine, it's all _fine,_ okay? I need to get back to work, because unlike here there's an _actual emergency_ taking place if I don't."

Her words did little to reassure the teachers or principal that they weren't witnessing some kind of Primal Alpha behavior. However, without reasonable evidence that _something_ was happening, there was very little they could do.

And so the rest of the school year passed in a haze of worry, fear, and nitroglycerin explosions.

0-0-0-0-0-0

Izuku knows the teachers think Katsuki must be crazy, acting like he is instead of kicking him to the curb. Truthfully he doesn't understand it completely himself; he only knows that things changed after he showed that book to Kacchan, and ever since then Kacchan's been pushing him to be _more,_ to do _better,_ to not tolerate all those who would shove Izuku around and tell him _you can't do this, you're Quirkless._

He knows Kacchan's friends don't like it, this change between them. He can feel and see the rift starting up between Kacchan and them, but every time he himself tries to step back and let Kacchan spend time with them, Kacchan tows him back in, relentless, as if he's afraid Izuku will run from him.

He wouldn't. He would never run from Kacchan.

So the rift is getting bigger with every day, and soon the whole thing is going to blow open, and words will be said that can't be taken back. Maybe that's what Kacchan's trying to prepare him for? The day when Kacchan turns his back on him and chooses his other friends - maybe he's just doing this to soften the blow, to make sure Izuku can stand on his own feet without crying too much.

 _Or maybe he's being honest,_ a little voice says. _Maybe he's doing this because he likes you, and he wants you to stay with him, because he's prideful and he wants you on his level._

Whatever the reason though, the teachers have watched them with dark eyes filled with worry, and several times one of them have made as if to intervene when Kacchan reaches out to grasp his wrist or hand or arm. He never hurts Izuku though, only tugs and demands his attention, an attention Izuku is finding easier to give by the day.

"Deku! Quit lazin' around and hurry up!" Izuku's attention snaps up, and he realizes with a start that class is over for the day, and Kacchan is impatiently tapping his foot as he waits by the front of the door, his other friends shifting nearby, glaring at him.

"O-oh, sorry! I'll be right there!" He hurriedly jams everything into his pack and rushes after them. As before Kacchan grabs his arm and tugs him up until he's on the other boy's right side, right by his elbow, just a step or two behind. The other boys are behind him, and anytime they try to get ahead of Kacchan or even Izuku they get glared at.

It must have to do with the book. _An Alpha's Guide to Care For Your Cluster_ sounds like something having to do with this - even though Izuku doesn't understand what a 'cluster' is, or why the advice in _that_ book in particular is so much more important than the advice in their history books that basically says Alphas are the ultimate predators, and should be respected as such, and Omegas are the providers, the caregivers, the baby-bearers. But it makes him feel good on some level to know Kacchan's not looking at him for any of those things.

He just wishes he knew what was in that book Kacchan keeps so close to him these days, or could at least read his mind, try to understand where he's coming from when he does these things like snarl at his friends or keep Izuku on his right side, or when he looks at Izuku like he's irritated and snaps like he's upset, but everything Izuku feels around him and sees in his body language says he's really not, he's just pretending. He wants to ask, to see if Kacchan will answer him.

He doesn't get a chance, not that night. They walk home, and Kacchan's other friends are unusually quiet, their stares boring into Izuku's back with a frightening intensity. When its their turn to peel off they do so reluctantly, eyes never leaving him as they go. The hairs on the back of his neck prickle as they vanish, but even long after they've gone he's left there feeling like there's a guillotine hanging over his neck, waiting to drop.

"C'mon idiot, move it." A light kick to his ankle gets him moving again. He glances over at Kacchan, hoping to catch his eye and inspire him to demand what Izuku wants - that never fails to start a conversation. But he's looking off in the other direction, gaze somewhere in the distance.

So Izuku goes home with questions burning in his throat, and hopes come tomorrow he will get the answers he needs.

0-0-0-0-0-0

Of course, even with such a simple, bare-bones plan, plenty can go wrong, and _does_ in fact, go wrong. The wordless, anxiety-fueled tension that Izuku's felt hovering over his head finally comes down with an almighty _snap,_ as Kacchan's friends ambush him in the spot where he normally meets Kacchan. Caught off his guard, and outnumbered, Izuku finds himself held down, kicked in the stomach repeatedly, and punched.

"This is your own fault, you know," one of them - Izuku can no longer remember names – jeers. "If you'd just disappeared properly like the worthless nothing you are, we wouldn't have to do this!"

There is blood rising in the back of Izuku's throat with every kick and punch they deliver. He struggles, tries to lash out _because Kacchan wouldn't want him to just sit and take it, he's_ _ **better**_ _than that,_ but four against one is not something he can overcome, and so in the end his struggles are in vain.

 _I'm sorry Kacchan,_ he thinks as his vision begins to grey - his head's throbbing and he feels dizzy, like he might pass out. There's a growing roar, like the rushing of waves in his ears, and then-

Kacchan is suddenly _there._

He seems to come out of nowhere, his Quirk exploding like fireworks. He nails the boy closest to Izuku with a punch directly to the face, kicks the second in the crotch hard enough to put him down, and then whips around to face the other two, snarl on his lips. He plants his feet on either side of Izuku's prone form, leans forward as his hands crackle with flame.

"What the actual fuck do you think you cowards are doing, huh?" His voice is low pitched, furious, which tells Izuku right away that this isn't a joke. "You think fucking four-on-one is _fair?!"_

"You're one to talk about _fair!_ You spend so much time with that useless Omega - what's gotten into you, Katsuki? How are we supposed to be a decent pack if you don't cut that weak tie loose?"

"That's not your call to make. And more importantly, I don't ever recall saying I'd ever form a pack with _you._ So why don't you lackluster extras get lost already, before you _really_ vex me?" His hands spark again, and the boys take a couple more steps back.

"You're making a mistake."

"Leave. _Now."_

They do, but the entire time they look at Katsuki like he's gone crazy. Izuku watches it all happen and feels a sense of guilt topple him. It's only once they're gone and Kacchan's knelt by his side that he speaks. "I'm sorry Kacchan."

"Huh? The heck are you apologizing for?"

"Y-you lost your friends because of me-"

A hand covers his mouth. For a second Izuku smells smoke and heat, but then it's gone. "Those extras weren't my _friends,_ Deku. You think I'd ever let idiots like _that_ into my pack? I'm better than that."

Izuku flinches. "O-oh. Yeah, that... makes sense I guess." He trails off, eyes on the ground. Kacchan hadn't mentioned _him_ specifically, but he knows he's not the smartest kid on the block, he's not on Kacchan's level certainly - and he's not strong or fast or capable of doing stuff so effortlessly. So in the end, even if Kacchan doesn't mention him by name, it basically amounts to him saying _you aren't worthy of being in my pack either,_ right?

"You're being stupid again, Deku," Kacchan snaps, evidently seeing his expression. "Stop overthinking it and just listen to what I'm about to say, 'cause I'm only gonna say it once. I don't waste my time with useless people, got it?" He forcefully tugs Izuku to his feet, smacking his shoulder to get him to stand up straight. "So hurry up and get on my level, you pansy. Now c'mon, we're late."

They start on back down the road that will take them to school, Izuku using some of the tissues he keeps in his bag to wipe the dirt and blood off himself. Trotting along behind Kacchan, he finally finds his voice to ask the question that's been bugging him. "Kacchan? What ever happened to that book we found in the library? The one about clusters?"

Kacchan doesn't turn around. "I have it with me. Why?"

"C-could I... um, when you're done with it, could I borrow it?"

He doesn't reply for a moment. Then, softer than anything Izuku's heard, "Do what you want." A hand digs into his bag, and the thick book is thrust at his face. "It's due next week, so don't you dare forget to hand it back when you're done with it, Deku."

He carefully takes it like it's made of glass. "Y-yes. Of course, Kacchan. Thank you."

"Whatever."

They do get in trouble for being late for class. Kacchan's friends also attempt to shoulder their way back over while he and Kacchan are quietly doing an art project together, only for Kacchan to send them a glare so blistering even Izuku feels its heat. They scurry back after that, though that doesn't stop them huddling together and glancing over occasionally, like they expect something to change.

It won't - Izuku can feel it now, the weight behind the blond's decision. He couldn't before because he'd been too wrapped up in the uncertainty of just what was happening, this strange balance Kacchan had been trying to make between them, but he feels it now, and he knows from experience Kacchan rarely changes his mind once he's made it up.

So he accepts it when Kacchan orders him to stay close on their way out the door, accepts it when Kacchan practically drags him behind him when the group tries _again_ to weedle Kacchan into shoving Izuku out of the picture, because he's a Quirkless Omega, and while being an Omega is all fine and dandy in this day and age, being Quirkless isn't.

Needless to say, the confrontation goes about as well as can be expected. Kacchan shows his temper yet again and the boys scurry off, and they head back home, the quiet between them semi-comfortable.

"Um," Izuku says as they near the point where they go their separate ways. "Thank you again Kacchan. For... everything." There's no adequate way to describe every little thing he wants to thank Kacchan for, not when it usually results in him rambling, and Kacchan telling him to shut up, so he sticks to the simplest way he can think of.

Kacchan rolls his eyes. "Whatever, you nerd. Just get that book back to me before the end of the week."

"Okay!"

And that's really all there is to say on the matter.

0-0-0-0-0-0

It takes Izuku two days and some change to read through the whole book. For once its thickness isn't a deception; the words are typed in 10 point font, so the pages are filled end to end, and there's about five hundred pages worth of content. Still, Izuku clears it in two days, and even manages to get a handful of important notes going about what it all boils down to, and what it means for him and Kacchan especially, because _that_ part at least is _extremely_ important.

Turns out what Kacchan's choosing to do with him isn't on a whim. The act of taking the weakest member of a Cluster - a group of two or more individuals with similar goals and a strong pack bond, which is what he and Katsuki technically are - and having the strongest member shove them around and basically push them up to the level of the strongest is called _breaking,_ and as morbid as it sounds, it's one of the healthiest, best things a cluster can do to keep itself going.

Old fashioned the book might be, but it's clearly written by someone who knew what they were talking about. They go into fine detail about the benefits versus the risks of cluster breaking, how important each aspect of the training is, and how while it may seem cruel to drag the weakest members to the attention of the strongest, it actually ensures that both sides come to a sort of mutual beneficial state.

Alphas are forced to recognize their own training methods up close and ensure that they don't harm the Omegas (which in this book, are usually mentioned as "the weakest") under their care, while the Omegas are brought up from a level they previously never assumed they would get out of, and forced into the spotlight and into a role of more independent thinking instead of mere subservience to the Alpha.

More importantly though, it builds a tighter bond between both sides, and prevents the cluster from falling apart due to internal or external weakness or aggression on either part. It isn't uncommon for cluster-mates to fall into bed together at some point, given that breaking typically acts as a type of extreme trust fall. According to the book, this is hardly a bad thing. Izuku doesn't go reading too much more into that section, instead flipping forward to see if he can find anything Kacchan might have considered important to read.

He finds sections he can imagine Kacchan reading. Sections that detail the proper type of role model any Alpha should strive to become, healthy interactions with cluster-mates, and the importance of reassuring the lower standing members often. This is the part that catches Izuku's eye, and the part where most of his notes end up coming from. It mentions greetings and goodbyes, and situations where Betas or Omegas end up hurting _worse_ because their Alpha refused to take a few simple moments to pull them closer and remind them that they were still alive and breathing.

 _ **Even if its merely a few words of kindness,**_ the book says, _**a little can go a long way! You must be aware of the emotional as well as the physical where it concerns your cluster, and take the necessary steps to keep your mates safe, happy and feeling as if they can trust you with anything. This is what it means to be an Alpha - to be the protector and provider for the cluster in all aspects.**_

It reminds him viscerally of the moment after Kacchan had chased his ex-friends off, how he'd told Izuku not to overthink, merely to _listen_ to his words and accept them. How oddly calm he'd been with the question about the book, and all the things he'd done to keep his ex-friends off Izuku's back these past couple of days. Kacchan, Izuku realizes, is already taking steps. Which means Izuku should too, because Kacchan is reaching out his hand in his own way, but he has yet to reach _back._

The book doesn't have any sections just about Omegas, or how Omegas should be good cluster-mates, but it has little points scattered here and there throughout the book, sections that mention what a healthy cluster will look like, and those are the parts Izuku eagerly copies down with shaking fingers, mind whirling a thousand miles a minute. With this, he thinks, he can become strong like Kacchan. All he has to do is follow the guidelines, and he can still be friends with Kacchan.

 _I need to talk to him,_ he thinks as he writes. _I need to make sure we're on the same page, that I'm not misinterpreting this all. Talking is important, right? So I'll talk to him._

He tries to plan out some semblance of how to go about that, just in case it _does_ turn out to be a misinterpretation and Kacchan was just feeling nice. If that's the case, he needs to apologize for bothering him, but... he doesn't think he's wrong about this. Still, just in case, he plans.

Of course, Fate laughs at men who plan. Walking to their usual spot, Izuku finds himself unreasonably nervous for some reason, his heart seeming to beat in triplicate when he finally spots Kacchan waiting for him. "Nerd," Kacchan greets him.

"H-hi Kacchan. Um. I finished the book!"

"Yeah?" Kacchan's gaze bores into him. "And what'd you think?"

 _Now or never._ He swallows, hard. "Um, d-d-do you- um, am I- um-" Kacchan's sharp sigh prompts him into finding his words before the boy can yell. "Am I in your cluster?"

The blond stares at him like he's just spoken Greek. "...you're just now figuring it out?"

"I didn't get a chance to read it before!" Izuku defends, missing the amused smirk on Katsuki's face. "I-I just saw the stuff you- or well, the stuff I _thought_ you'd read last night, and I put two and two together, but I wanted to make sure it was okay and that I didn't misjudge the situation and accidentally accuse you of-"

A hand slaps over his mouth. Kacchan's shoulders are shaking, his eyes bright and a smirk on his face.

"Do you _ever_ shut up, nerd?"

Izuku realizes he's been ranting again. "Sorry," he mumbles against Katsuki's palm. When Kacchan pulls away and Izuku licks his lips, he tastes smoke and salt. But his mouth isn't blistered from heat, so that's a plus. "S-s-so you're trying to break me, right?"

Kacchan nods. "Yeah. You're nowhere near my level yet Deku, but I'll make sure you will be. I won't be drug down by someone who's a doormat, so you'd better not wimp out." A burst of fire comes from his palms, startling Izuku. "Got it?"

He nods, hastily. "O-of course! I just, um... Uh." Something else comes into his mind, and he sucks in a deep breath. "As your cluster-mate, I haven't greeted you properly."

Kacchan freezes. For one horrible second, Izuku thinks _this is it, I've overstepped again, good going idiot,_ but Katsuki relaxes before his tirade can kick off. "You don't have to," he says quietly. "It's not required."

"I know," Izuku says, equally quiet. He finds his eyes drawn to the ground, and forces himself not to shy away from this. He'd gotten plenty embarrassed about it last night, but his resolve has solidified. If Kacchan's going by the book, he will too. They'll be fine. "I want to, though. Not because you're an Alpha who's so much stronger than me, but because you're Kacchan. You're amazing to me, and I want to show you that. S-so, um-"

"Do what you want," Kacchan interrupts, gaze swerving off to the side. The tips of his ears have gone red. "Just hurry up already and do it if you're gonna do it, you nerd, or we'll get yelled at _again,_ and this time I'll really smack you."

"Y-yes, okay then. P-please stay still."

Izuku scrubs his palms against his jeans as he moves forward, until he and Kacchan are right in each other's personal spaces. Kacchan's still looking off to the side, but Izuku can see the tension in his shoulders and neck, and its making him feel like a bomb ready to go off. He leans his face over and presses their cheeks together, making a smooth, even circle before pulling back.

A greeting, according to the book, between cluster-mates. _Hello, are you well, I come in peace._ Also a reassurance, if the gesture moves from higher-ranking to lower-ranking among the cluster.

"Okay?" he asks quietly, when Kacchan still hasn't moved afterwards. The tension's going away though, slowly. "Kacc-?"

Kacchan suddenly reaches out and pulls him in, performing the same gesture to him - and this time it's undoubtedly a reassurance. The movements are slow and easy and gentler than Kacchan's been to him in a while, but more to the point, he's keeping eye contact, or as much as he can while he moves. Izuku feels his own shoulders slump as he leans into the movement, an unconscious decision he doesn't attempt to correct. When Kacchan finally steps back, Izuku feels oddly cold.

"C'mon, we're gonna be late," Kacchan says. The tension in his body is gone.

They manage to make it on time, if only by a few precious seconds. As they settle down in their seats, he catches Kacchan looking at him out of the corner of his eye, and then glancing over to the far corner, where his former friends are hunched together, watching Kacchan as usual. This time however, their presence doesn't bring that feeling of anxiety to Izuku's mind. They're simply _there,_ avoidable, non-intrusive. They don't matter to him, or to Kacchan.

 _I think I'm going to be okay,_ he writes to Kacchan on a small scrap of paper, and flicks it over when the teacher isn't looking. An equally small paper comes back at him moments later.

 _Course you will. You're with me, right?_

 _Yeah,_ Izuku thinks, tucking the paper into his palm and focusing on the lecture. _I am._


End file.
